Vegetable glue and method of making the same



Patented Jan. 7, 1947 VEGETABLE GLUE AND METHOD OF MAKING THE SAME Gordon G. Pierson, Lansdale, Pa., assignor to Perkins Glue Company, Lansdale, Pa.., a corporation of Delaware No Drawing. Application October 26, 1943,

Serial No. 507,722

Claims. 1

The present invention relates to a novel vegetable glue of advantageous properties and to an economical method of preparing the same. The present application is filed as a continuation-inpart of my copending application Serial No. 495,889, filed July-23, 1943.

Heretofore, various starches have been used or proposed for use in the preparation of vegetable glues for wood-working'purposes, including cassava, corn, potato, and sago starch. Such starches have been converted into glue by bursting them, with or without peroxides, copper salts, and other modifying agents, in a solution of caustic soda and water by well known and standard procedures. Starch glues for wood-working purposes must possess certain characteristics in order to be used successfully. For example, they must not carry excessive amounts of water or caustic soda and must have a relatively heavy body in order to prevent excessive penetration. Such heavy-bodied. glues must, however, flow readily from containers and pipes and must main tain a reasonable degree of stability, as shown by the continued fluidity thereof, over a period of several hours. In addition, the consistency of the glue must be such that it i easily and smoothly applied from spreader rolls to veneer sheets in a smooth, continuous layer of suitable thickness.

It will be seen from the above that the fluidity of the glue at the time of its preparation and at least for everal hours thereafter is an important characteristic. It is known that the fluidity of the glue varies with the water content thereof; the lower the water content, the less fluid is the glue. However, the use of excessive water cannot be relied upon to increase the fluidity of the glue, since excessive water facilitates penetration of the glue too deeply into the wood, thus producing weak or starved joints. Water introduced into the Wood by the gluing operation i the principal factor causing warping, checking, staining, slow-setting, molding, and other diificulties commonly known to the wood-worker. Furthermore, the manufacturer of plywood considers. it necessary or desirable. to eliminate from the glued-up wood constructions, beforethe article is finally assembled and finished, nearly all of the water which has been. added in the gluing operation. This i usually done by means of a dry kiln or by long exposure under normal room atmospheric conditions. For these reasons, the water content of vegetable glues have been kept as low as possible commensurate with the particular requirements of the glue.

Furthermore, as pointed out above, vegetable glues should maintain a reasonable degree of stability, that is should maintain the desired fluidity, over a period of several hours in order to insure that they may be flowed from containers and pipes and be utilized in commercial glue spreading equipment. The vegetable glues heretofore produced have frequently possessed the tendency to thicken upon standing and, hence, their application to the products to be glued have at times presented difiiculties.

One object of the present invention isto provide a vegetable glue having increased fluidity and stability as compared to the usual glues of the same water content and possessing the recited characteristics which are necessary for a successful vegetable glue in the wood-working trade.

A further object of the invention is to provide a vegetable glue having a low water content and characterized by satisfactory fluidity and stability and improved consistency.

Other objects, including the provision of a, novel and economical method of producing the glue of the present invention, will be apparent from a consideration of this specification and claims.

While the present invention will be described with particular reference to a glue for the .woodworking trade, it is to be understood that the glue of the invention may be used for any purpose where a glue of the properties described is desired.

The vegetable glue base of the present invention comprises starch and a, small amount of a finely divided calcium compound furnishing calcium ions in the presence of water, and possessing the property of liqueiying and stabilizing the starch glue during the conversion of the glue base into glue and for an appreciable time thereafter to insure satisfactory working life thereof. In converting the glue base into the glue, the base is treated with caustic alkali and water under conditions causing the starch grains. to burst and to form a glue of the required consistency. The bursting of the starch granules exposes the interior as well as the exterior of the granules to reaction with the ingredients of the glue mix. It is to be understood that, instead of forming a glue base, the starch, the calcium compound, the caustic alkali, the water, and any other ingredients may be mixed together at the time the vegetable glue is produced.

Although various liquefying and stabilizing agents have been proposed for use in vegetable glues, the calcium compounds used in accordance with the present invention have marked advantages thereover; for example, the calcium compounds do not decompose and are, therefore, effective over an extended period, they do not discolor the glue or the glued article, and they are useable in such small amounts that the glue is not adulterated or rendered hydroscopic thereby.

The starch employed in the preparation of the glue base or glue may be any starch-containing (amylaceous) material, but the starch employed is advantageously one in which the starch granules have not been burst by chemical or physical action. The liquefying and stabilizing effects produced by the calcium compound are most marked when a raw starch, that is an unmodified starch, is employed, and since these starches are more economical than modified starches, they will generally be employed in practicing the invention.

The starch component of the vegetable glue base or of the glue may be a single amylaceous material or a mixture of amylaceous materials. Examples of starches that may be employed alone or in admixture with each other are cassava starch, potato starch, rice starch, sago starch, corn starch, wheat fiour, rye flour, and the like. It will be understood that the properties of the glue and the degree of improvement resulting from the use of the calcium compound will be dependent upon the particular starch or mixture of starches employed. A particularly advantageous vegetable glue is obtained by the use of a calcium compound as herein described with mixtures of cassava starch and some other amylaceou material such as corn starch, wheat flour, potato flour, and the like.

The calcium compound employed, as previously stated, is sufficiently soluble to provide a significant amount of calcium ions when mixed with water and possesses the property of liquefying and stabilizing the starch glue when the starch is burst in the presence of caustic alkali and water. The term "liquefying refers to the ability of the calcium compound to bring about a reduction in the viscosity or water-absorptive capacity of the glue; and the term stabilizing refers to the ability of the calcium compound to prevent or retard the thickening action of the glue. The calcium compound is preferably finely divided and may be the hydroxide, peroxide, or oxide, or a salt of an organic or inorganic acid, such as the acetate, chloride, nitrate, iodide, bromide, ferrocyanide, hypochlorite, citrate, formate, lactate, and the like. It is to be understood that the compounds named are merely illustrative, and that any other calcium compound possessing the properties stated may be employed. If a calcium salt is employed, the anion of the salt is relatively unimportant so long as it does not possess a coagulating effect which would counteract the desired liquefying and stabilizing effects. Of the various calcium compounds available for use, calcium hydroxide is preferred. When a peroxide is to be employed, calcium peroxide may be used to provide all or a portion of the calcium ions and of the oxidizing action. When a calcium salt is employed, the use of a non-hydroscopic salt is recommended. If a peroxide is employed, a calcium salt will advantageously be selected which does not destroy the beneficial efi'ects of the peroxide.

The calcium compound is present in amounts sufficient to liquefy and stabilize the starch and the amount employed is below that which will exert a thickening or coagulating effect on the starch. In general, the calcium compound is present in a small amount based on the total weight of the starch content, for examp ro about 0.1% to about 1.0% calculated as Ca(OH)z, about 0.3% to 0.5% being preferred. In the case of the use of a finely divided, active calcium hydrate, the amount employed will usually not exceed 0.8%. When a calcium salt is employed, the actual amount employed may, of course, be correspondingly higher, but for convenience, the figures have been given on the amount of calcium compound calculated as Ca(OH)-z by weight based on the total weight of the starch content.

In some instances, a small amount of a peroxide may be present at the time of the conversion of the glue base into the glue, in order to improve the properties of the glue, for example, to provide a glue with even a lower water ratio. If the peroxide is stable in the presence of the dry starch and calcium compound, it is advanta geously mixed with these ingredients, and thus becomes a component of the dry glue base. If desired, the peroxide may be added at the time of the conversion of the glue base into the glue. If a peroxide is employed, it is generally present, in amounts between about 0.1% to about 2.0% by weight based on the weight of the total starch content, preferably between 0.4% to 1.0%. The use of barium peroxide is preferred, but as pointed out, calcium peroxide may be used to supply both the calcium ions and the oxidizing effect. If the peroxide is not to be added until the glue is prepared, the stability of the peroxide is relatively immaterial, and, therefore, such peroxides as hydrogen peroxide, sodium peroxide, and the like may be used.

The calcium compound in addition to functioning as a liquefying and stabilizing agent, possesses a catalytic effect, when a peroxide is also employed, in reducing the time and temperature requirements in the preparation of the glue. When starch is burst with caustic alkali in the presence of an active peroxide, the consistency of the glue depends both upon the temperature of the treatment and the time over which the temperature is applied. Furthermore, independently of the nature and consistency of the glue produced by the conversion, it is always an advantage to consume a minimum of time or heat or both. The use of the calcium compound has been found to reduce considerably both the time and the temperature required for the conversion and for this reason a glue of improved consistency is produced.

In preparing the glue, the starch, or plurality of starches, the calcium compound, and any modifying ingredient such as the peroxide, either as a preformed glue base or as separate ingredients, are placed in a glue kettle with caustic alkali and water and the mixture is agitated and reacted. The temperature and time of treatment may be varied as desired, but these conditions are selected to give a burst starch product. In general, the greater the amount of caustic alkali employed, the lower the temperature required, except in those cases where a peroxide is used. In such cases, as stated, the calcium compound acts advantageously so that the temperature required may be much lower than would otherwise be the case. The caustic alkali is advantageously caustic soda but caustic potash may be employed if desired. The amount of caustic alkali employed will be sufficient to burst the starch material, but will advantageously not be present in a large excess, for example, when the glue is to be employed in the wood-working trade, the amount of caustic alkali employed will not be sufficient to cause excessive staining of the wood glued by the product. Generally, the amount of caustic alkali employed will be between about 1% and 12%. The ratio of water to the solid content of the glue may vary as desired, depending on the particular use for which the prepared glue is intended. In the wood-working trade, the use of a relatively low water ratio is desired and generally it will be less than 4 to l, but may be much lower.

In forming a glue base, the starch, or a plurality of starches, the calcium compound, the stable peroxide (if employed), and any other ingredients may be intimately mixed in the dry state. This glue base may be sold and shipped to users, who will convert it, prior to use, into the glue by treatment of the base with caustic alkali and water. Typical examples of glue bases of the invention are illustrated in the following table, and for convenience there is also included in the table the amount of water and caustic soda and the temperature employed in converting the glue base into the glue using conventional equipment:

As pointed out, instead of preforming a glue base, the various ingredients may be mixed in the equipment in which the glue is formed. It i to be understood that the above are merely examples and that various other starches or mixtures of starches may be employed and that the ingredients and temperature employed may also be varied.

I claim:

1. A liquefied and stabilized vegetable glue comprising burst starch in water in a ratio of water to burst starch of less than 4 to 1, the said product being the reaction product of a mixture substantially free from materials possessing a coagulating and thickening action on said glue and comprising unburst starch, caustic alkali in an amount to burst said starch between about 1% and about 12% by weight based on the weight of the starch, water, and a calcium compound furnishing calcium ions possessing the property of liquefying and stabilizing the glue in an amount between about 0.1% and about 1.0% by weight calculated as calcium hydrate and based on the weight of the starch.

2. The product of claim 1 wherein the ratio of water to burst starch is not more than 2.25 to 1, wherein the calcium compound is finely divided calcium hydroxide, wherein the starch of the reacted mixture is unmodified starch, and wherein the caustic alkali is caustic soda.

3. A liquefied and stabilized vegetable glue comprising burst starch in water in a ratio of water to burst starch of less than 4 to 1, the said product being the reaction product of a mixture substantially free from materials possessing a coagulating and thickening action on said glue and comprising unburst starch, caustic alkali in an amount to burst said starch between about 1% and about 12% by weight based on the weight of the starch, water, a calcium compound furnishing calcium ions possessing the property of liquefying and stabilizing the glue in an amount between about 0.1% and about 1.0% by weight calculated as calcium hydrate and based on the weight of the starch, and a peroxide in an amount between about 0.1% and about 2%.

4. The product of claim 3 wherein the ratio of water to burst starch is not more than 2.25 to 1, wherein the calcium compound is finely divided calcium hydroxide, wherein the starch of the reacted mixture is unmodified cassava starch, and where the caustic alkali is caustic soda.

5. The method of preparing a liquefied and stabilized vegetable glue comprising burst starch in Water in a ratio of water to burst starch of less than 4 to 1, which comprises agitating together a mixture substantially free from materials possessing a coagulating and thickening action on said glue and comprising unburst starch, caustic alkali in an amount to burst said starch between about 1% and about 12% by weight based on the weight of the starch, a calcium compound furnishing calcium ions possessing the property of liquefying and stabilizing the glue in an amount between about 0.1% and about 1.0% by weight calculated as calcium hydrate and based on the weight of the starch, and water in an amount to provide said water-to-starch ratio, and heating said mixture to burst said starch to provide said liquefied and stabilized vegetable glue.

6. The method of preparing a liquefied and stabilized vegetable glue comprising burst starch in water in a ratio of water to burst starch of less than 4 to 1, which comprises agitating together a mixture substantially free from materials possessing a coagulating and thickening action on said glue and comprising unburst starch, caustic alkali in an amount to burst said starch between about 1% and about 12% by weight based on the weight of the starch, a calcium compound furnishing calcium ions possessing the property of liquefying and stabilizing the glue in an amount between 0.1% and about 1.0% by weight calculated as calcium hydrate and based on the weight of the starch, a peroxide in an amount between about 0.1% and about 2.0%, and Water in an amount to provide said water-to-starch ratio, and heating said mixture to burst said starch to provide said liquefied and stabilized vegetable glue.

7. The product of claim 1 wherein the calcium compound is finely divided calcium hydroxide and wherein the caustic alkali is caustic soda.

8. The product of claim 3 wherein the calcium compound is finely divided calcium hydroxide and wherein the caustic alkali is caustic soda.

9. The method of claim 5 wherein the calcium compound is finely divided calcium hydroxide and wherein the caustic alkali is caustic soda.

10. The method of claim 6 wherein the calcium compound is finely divided calcium hydroxide and wherein the caustic alkali is caustic soda.

GORDON G. PIERSON. 

